Flameproof delay composition with a delayed-action time in the millisecond range



11 Claims. 61. 149-40 This invention relates to delay compositions having delayed-action times in the millisecond range. More particularly, it relates to flameproof delay compositons with a delay in the millisecond range which consist essentially of an oxidizable metal, an oxidizing agent, and a metallic ballast material. Even more particularly, the invention relates to flameproof delay compositions having a delay time in the millisecond range which consist essentially of an oxidizable metal, an oxidizing agent, and a metallic ballast material and which, because of the particular metals chosen as the ballast material, will not ignite explosive atmospheres or firedamps when burned because of their relatively low heat and temperature of combustion.

Delay compositions are used, for example, in delay electric blasting caps which essentially comprise an ignition charge, a detonating charge and a delay element through the medium of which the detonating charge is fired. The delay element is customarily a fuse of such length and composition as will afford the desired delay interval between firing of the ignition and detonating charges. Such explosive means have found wide use in mining and quarrying operations to provide sequential initiation of the explosive charges in an array of boreholes. By such sequential initiation, an eit'icient blasting action with respect to the amount of material blasted in one operation and to the degree of fragmentation of the material blasted can be achieved.

The delay compositions of the present invention are those which have become known in the art as delay com positions with short delay periods, i.e., wherein the period of delay is measured in terms of milliseconds.

Such compositions are used as delay elements especially for electrical time fuses which are gasless and possess explosive power.

Mixtures consisting of silicon and lead oxide are generally used for delay compositions having delayed-action times in the millisecond range. In mixtures wherein the proportion of silicon is relatively low, the combustion heat of the composition is extremely high. Thus, very high temperatures occur in the combustion zone, resulting in the danger of ignition of explosive atmospheres or firedamps present therein. As known in the art, firedamps are combustible gases or damps, usually formed in mines by the decomposition of coal or other carbonaceous matte-r, consisting chiefly of methane. An explosive mixture is formed by the mixture of such gases with air.

In order to avoid the ignition of such explosive atmospheres or firedamps by hot-burning delay compositions, several measures have been employed in the past. One of these measures, for example, consists in preventing the discharge of glowing slag during the detonation of the fuse by arranging the delay composition and the explosive charge of the fuse separately from each other so that they are brought into contact with each other only through a narrow and sulficiently long channel. Another known measure involves providing a pressure equalization between the gases given off by the delay composition and the explosive charge of the fuse by the use of gas-permeable masses into which the delay composition is introed States Patent duced. This technique prevents the blowing out of any particles of hot slag from the burned-off delay composition.

The present invention is directed to a different solution to the problem of eliminating the danger of igniting firedamp mixtures when using such delay compositions. The concept behind the present invention is the recognition that it is more expedient and safe to strip the slag itself, which is formed during the burning of the delay composition, of its capacity to ignite firedamp mixtures, rather than to strive only to prevent, by employing corresponding counter-measures, the disadvantageous consequences which could result from the potential danger inherent in the slag.

The cause of the ignition of firedamps or other explosive atmospheres during the use of the conventional millisecond delay compositions of silicon and lead oxide lies in the aforementioned high temperature of burning of these delay compositions as well as the very strong afiinity for oxygen of the excess silicon present in these compositions. A decrease of the combustion temperature, which may be effected, for example, by increasing the silicon content of the delay composition, is possible only to a limited extent because the combustion time then becomes too long if a certain limit is exceeded. Moreover, the use of activated silicon with the object of rendering possible an increased silicon content in the composition, thus maintaining a constant combustion time for the composition, may be realized only to a limited extent since excess activated silicon is particularly dangerous with respect to igniting firedamps. 7

Accordingly, one of the objects of the present invention is to provide a delay composition having a delay-action time in the millisecond range which overcomes the disadvantages and deficiencies of the prior art compositions.

Another object of the present invention is to provide a delay composition which will not ignite explosive atmospheres or firedamps by virtue of its relatively low heat and temperature of combustion.

A further object of the invention is to provide a delay composition which will not ignite explosive atmospheres or firedamps because of the properties of the delay composition itself, thus obviating the need for complex-prior preventive measures, as employed with the prior art compositions.

These and other objects of the present invention will become apparent to those skilled in the art from a reading of the following specification and claims.

In accordance with the present invention, adifferent approach is chosen in that a delay composition consisting essentially of an oxidizable metal or metalloid and oxidizing agents therefor is provided, wherein the excess oxidizable metal or metalloid present in the composition is replaced by a corresponding amount of a metallic ballast.

material. The metallic ballast material added to the delay composition is one which has a thermal conductivity of greater than 0.5 and/or which forms with the oxidizable metal an alloy the eutectic point of which is less than 1300 C. and which has a heat of formation of its oxide of less than 1200 calories per gram. Such a composition, for example, one based on a silicon-lead oxide mixture, has a delayed-action time in the millisecond range, while overcoming the disadvantages of the prior art compositions mentioned hereinabove.

Experiments have shown that a delay composition of, for example, a mixture of 25% fine silicon and red lead (Pb O burnsover a burning path of 20 mm. for about milliseconds. The burning time can be extended to a desired value of, for example, 300 milliseconds if 70% by weight, based on the amount of the mixture, of copper powder is added to the mixture. The combustion heat is thereby reduced by almost half, and the comfor the intended purpose of the present invention.

bustion temperature is also reduced almost to the same extent.

The delay compositions of the present invention are readily prepared by means well known in the art. The components of the delay compositions are generally used in the form of powders and are thoroughly mixed together by well known methods.

Instead of copper, other metallic powders may be utilized. Copper is particularly suitable since it has a thermal conductivity of more than 0.5 and forms an alloy with silicon the eutectic point of which is below 1300 C. and, which, during the formation of its oxide, gives olf a heat of less than 1200 calories per gram. If only the requirement that the ballast material possess a thermal conductivity of more than 0.5 is to be satisfied, aluminum, silver and antimony, for example, are also suitable. If, instead, the thermal conductivity of the metal is to be disregarded and if, for the purpose of reducing the ignition danger posed by the excess silicon present in delay compositions, the only requirement sought to be met is that the ballast material form with the oxidizable metal of the delay compositions alloys whose eutectic points are below 1300 C. and that the ballast material have a heat of formation of its oxide of less than 1200 calories per gram, then nickel and iron, for example, have also been found to be advantageous and fully appropriate The silicon-red lead delay compositions of the present invention may contain from to 50% by weight of silicon, from 25 to 75 by weight of red lead and from 50 to 10% by weight of the metallic ballast material. Such delay compositions in the millisecond range are well known in the art.

The silicon-lead dioxide delay compositions of the present invention may contain from 20 to 70% by weight of silicon, from to 70% by weight of lead dioxide and from 50 to 10% by weight of the metallic ballast material. Such delay compositions in the millisecond range are well known in the art.

The metallic ballast material has been described as being in the form of a powder. Preferably, a particle size of metallic ballast powder of less than 40p. gives exceptionally good results.

The above mentioned lead oxides are chiefly lead dioxide and red lead. Lead monoxide (PbO) is only of minor importance.

The following examples are given merely for purposes of illustration and are not to be considered as limiting.

The mentioned combustion period was taken on brass samples having a length of 25 mm., a diameter of 6.4 mm. with a hole of 3.3 mm. The delay compositions were pressed into the hole with a pressure of about 1000 The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention and all such modifications are intended to be included within the scope of the following claims.

I claim:

1. Delay composition having a delayed-action time in the millisecond range consisting essentially of powdered silicon, an oxidizing agent selected from the group consisting of the oxides of lead, and a pulverulent metallic ballast material, said metallic ballast material being characterized in having a thermal conductivity of greater than 0.5, in forming with said oxidizable metal an alloy the eutectic point of which is less than 1300 C. and in having a heat of formation of its oxide which is less than 1200 calories per gram.

2. The delay composition of claim 1, wherein the oxidizing agent is red lead.

3. The delay composition of claim 2, wherein the metallic ballast material is copper.

4. The delay composition of claim 1, wherein the oxidizing agent is lead dioxide.

5. The delay composition of claim 2, wherein said delay composition consists essentially of from 10 to by weight of silicon, from 25 to 75% by weight of red lead and from 50 to 10% by Weight of said metallic ballast material.

6. The delay composition of claim 4, wherein the metallic ballast material is copper.

7. The delay composition of claim 4, wherein said delay composition consists essentially of from 20 to 70% by weight of silicon, from 15 to 70% by weight of lead dioxide and from 50 to 10% by Weight of said metallic ballast material.

8. A powdered delay composition having a delayedaction time in the millisecond range consisting essentially of approximately 15% by weight of silicon, approximately 44% by weight of red lead, and approximately 41% by weight of copper.

9. Delay composition having a delayed-action time in the millisecond range consisting essentially of powdered silicon, an oxidizing agent selected from the group consisting of the oxides of lead and pulverulent silver.

10. Delay composition having a delayed-action time in the millisecond range consisting essentially of powdered silicon, an oxidizing agent selected from the group consisting of the oxides of lead and pulverulent antimony.

11. Delay com-position having a delayed-action time in the millisecond range consisting essentially of powdered silicon, an oxidizing agent selected from the group consisting of the oxides of lead and pulverulent nickel.

kg./cm. (References on following page) Silicon, Cu-powder, Pb Oz Nitrocellulose Millfineness of grain, fineness of grain, in varnish in CaL/g. seconds 20p in percent 30n in percent percent percent Substitute metal, fineness of grain, 30 in percent 45 Niz27 28 0. 1 147. 4 533 45 Agz27 28 0. 1 148. 7 287 45 Sb:27 28 O. 1 158. 0 407 45 011:27 28 0. 1 182. 9 363 References Cited UNITED STATES PATENTS 5/1931 Ha'le 149--44 9/1932 Hale 14937 5 6/1937 Burrows et a1. 149--37 7/1951 Kerr et a1. 149'-37 6 Kerr et a1. 149-37 Lewis 14937 Ball et a1. 149-37 Ball at al'. 14937 BENJAMIN R. PADGE'IT, Primary Examiner.

S. J. LECHERT, ]R., Assistant Examiner. 

1. DELAY COMPOSITION HAVING A DELAYED-ACTION TIME IN THE MILLISECOND RANGE CONSISTING ESSENTIALLY OF POWDERED SILICON, AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF THE OXIDES OF LEAD, AND A PULVERULENT METALLIC BALLAST MATERIAL, SAID METALLIC BALLAST MATERIAL BEING CHARACTERIZED IN HAVING A THERMAL CONDUCTIVITY OF GREATER THAN 0.5, IN FORMING WITH SAID OXIDIZABLE METAL AN ALLOY THE EUTECTIC POINT OF WHICH IS LESS THAN 1300*C. AND IN HAVING A HEAT OF FORMATION OF ITS OXIDE WHICH IS LESS THAN 1200 CALORIES PER GRAM. 